1. Field of the Invention
The invention relates to a method for forming an iron sprayed coating formed with a wire for arc spraying by melting the wire for arc spraying by means of an electric arc and spraying the molten wire for arc spraying to a substrate while supplying compressed gas to the molten wire, and to a member with the iron sprayed coating which includes a substrate coated with the iron sprayed coating.
2. Description of Related Art
Internal surfaces of cylinder bores of cylinder blocks are coated with sprayed coatings formed by the spraying technique involving instantaneous melting of various metals or alloy metals by means of flames generated with an arc, plasma or gas and allowing collision/solidification and attachment of the sprayed particles atomized (rendered to be fine particles) by means of compressed gas, in order to improve corrosion resistance, wear resistance and the like of the internal surfaces of the bores.
For example, Japanese Patent Application Publication No. 2009-155720 (JP 2009-155720 A) discloses an exemplary technique of a method for forming a sprayed coating by plasma spraying using a material containing 0.12% by mass or more of carbon. For example, Japanese Patent Application Publication No. 2010-275581 (JP 2010-275581 A) discloses a method for forming a sprayed coating containing, in mass ratio, 0.3 to 0.4% of C, 0.2 to 0.5% of Si, 0.3 to 1.5% of Mn and 0.5% or less of Cr and/or Mo in total with the balance being Fe and unavoidable impurities.
Although use of materials containing an increased amount of carbon as JP 2009-155720 A and JP 2010-275581 A may improve wear resistance of the sprayed coatings, it may also decrease machinability of the sprayed coatings. When arc spraying is carried out with wires for arc spraying containing an increased amount of carbon, the strength of the wires themselves may be improved, thereby decreasing the productivity.
With the above in mind, Japanese Patent Application Publication No. 2008-240029 (JP 2008-240029 A) discloses a method for forming a sprayed coating using a wire for arc spraying containing a main component of Fe, 0.01 to 0.2% by weight of C and 0.25 to 1.7% by weight of Si. In this method, the sprayed coating is formed by melting the wire for arc spraying by means of an electric arc and spraying the molten wire for arc spraying on a substrate while supplying compressed air to the molten wire.
However, the method of forming a coating disclosed in JP 2008-240029 A may result in a decreased adhesion strength between the sprayed coating and the substrate because spraying is carried out with air containing oxygen. Specifically, use of oxygen-containing gas results in attachment on the substrate of not only the iron oxide that forms the coating but also fine iron oxide dust. The presence of the attached substances on the substrate between the coating and the substrate is considered to decrease the metallic attachment or anchor effect between the coating and the substrate. This phenomenon is more significantly manifested when spraying is carried out using the materials disclosed in JP 2009-155720 A and JP 2010-275581 A.